Free-flowing cyanuric acid



United States This invention relates to free-flowing cyanuric acid. More particularly, it relates to a dense, granular, freeflowing cyanuric acid product, and to the process of producing it.

In recent years the role of cyanuric acid in the chemical industry has become increasingly important. Applications calling for its use are being developed in many areas, including resins and chlorinated cleaning compositions. With the increased use of this material in varying amounts, packaging and, consequently, the physical characteristics of the cyanuric acid have become important considerations. Cyanuric acid in the form of a fine powder is unsuitable for packaging in small containers using automatic equipment, and packaging even in large containers is difiicult. The tendency of such material to cake, stick and lump results in fouling of packagin equipment and in packages in which the contents are lumpy and non-uniform. Furthermore, the lack of mobility, i.e. ability to flow through an orifice of a certain diameter at a given rate, increases the filling time per container and thus adds to the ultimate cost of the material. In addition, persons working with such packaging equipment may be bothered by the fine particles of cyanuric acid which have a tendency to get into the surrounding atmosphere.

in view of the foregoing, it is an object of the present invention to provide a novel cyanuric acid product which is noncaking, free-flowing, dust-free and suitable for automatic packaging.

It is a further obiect of the present invention to provide a process for producing such a product.

The product of this invention is a body of granular cyanuric acid aggregates having a bulk density of about 0.9 to 1.0 gram per cubic centimeter, and a mobility, as hereinafter defined, not exceeding 15 seconds, preferably not exceeding seconds.

The product of this invention is obtained by a process which comprises passing finely divided cyanuric acid between rollers exerting a pressure on the cyanuric acid of at least 25,000 p.s.i., breaking the resulting compacted material into small pieces, and air-separating from fines a high-fiow granular product.

The cyanuric acid fed to the compactor must be fine enough so that at least 70% by weight is capable of passing through a 200 U.S. mesh screen, and preferably fine enough so that 80% can pass through such a screen. If the particle size of cyanuric acid feed is larger than specified, the final product will be soft and dusty.

The cyanuric acid feed should contain less than 0.3% by weight, and preferably less than 0.2% moisture, to enable the final product to maintain free-flowing properties after extended storage periods. Presence of small amounts of water-soluble salts in the powdered cyanuric acid feed must be kept to a minimum. For example, concentrations of 500 ppm. or more of ammonium sulphate or ammonium nitrate, which compounds may be formed during the purification procedure, have a deleterious effeet on the flow properties of the cyanuric acid product during storage.

Pressure on the compacting rolls at the line of contact of rolls and powder must be high, at least 25,000 p.s.i. and preferably 60,000 to 80,000 psi. Lower pressures atent result in a product which is soft, has a tendency to dust, and has poor flow characteristics. Other types of compactors, such as extrusion devices, give a cyanuric acid product of sufficient hardness only when the cyanuric acid contains appreciable moisture, e.g. 1% or more, and the product with such a high moisture content will not have the desired flow properties. It is preferred to use a compactor having grooved rollers, the grooves running in the direction of rotation of the rollers and containing frequent breaks to allow escape of air during compaction. Size of the rollers is not critical, but high pressure dictates that they be relatively small. Best results are obtained with rollers 6 to 10 inches in diameter and 6 to 10 inches long.

Air classification of the product is necessary to give a dust-free product having satisfactory mobility as hereinafter defined. Ordinary mechanical means of size classification such as screening are unsatisfactory, and give poor flow grades unsuitable for automatic package-filling devices. Presence of small amounts of dust (material finer than 300 US. mesh) in the product not only results in poor working conditions for packaging workers, but decreases product mobility. Cyanuric acid with the desired mobility may be produced with use of only one air separator, but two are preferred; one to remove oversized particles, and the second to remove dust. When only one air separator is used it is necessary that the compacted product be granulated to a finer condition so that essentially no oversized particles are in the product. This produces considerably more cyanuric acid dust, thereby increasing dust recycle and reducing the capacity of the air separator. While it is not possible to obtain satisfactory product with dust removal by screening, a combination of mechanical and air separators can be used. Coarse particles may be mechanically screened from granulated product for recycle with the smaller particles air separated for recycle. The ratio of coarse recycle to fresh feed must be controlled so that at least by weight of the material entering the compactor can pass through a 200 US. mesh screen.

In order to assure the desired mobility, less than 2% by weight of the compacted, air-classified cyanuric acid product should pass through a 300 US. mesh screen and preferably the product is substantially free of such dust.

By mobility is meant the time required for 250 grams of material to flow from a funnel having a 60 lip angle, a 192 mm. internal funnel diameter, a 150 mm. stern' length and a 15 mm. internal stern diameter. The method used for determining this mobility is similar to ASTM 13392-38.

Another convenient method for characterizing the flowing and non-caking properties of cyanuric acid is by flow grade. The following test procedure has been devised for determining the flow grades. grams of cyanuric acid sample is introduced into a one-pint Mason jar which is then closed. The jar is rotated on a horizontal axis at a rate of 5 rpm. and the behavior of the solids during rotation is observed. Ratings for several flow grades are assigned as follows:

Flow grade: Description 1 Excellent flow characteristics, free flowing individual particles break away from main body of particles and roll at leading edge of mass on rotating wall.

2 Very good flow characteristics, free flowing, cyanuric acid breaks away from wall at leading edge of mass in about /s%" increments and then particles roll as in- Description dividual particles until resubmerged into main body of particles.

3 Good flow characteristics, free flowing, cyanuric acid breaks away, from wall at leading edge of mass in about /2" increments and then particles roll as individual particles until resubmerged into main body of particles.

4 Fair flow characteristics, cyanuric acid breaking away from wall at at leading edge of mass in sizable pieces. Part of the pieces break up but some soft lumps remain in rotating main body of particles.

5 Poor flow characteristics, cyanuric :acid

turns over in irregular lumpy fashion,

some free individual particles exist but soft lumps are distributed throughout the mixture.

Flow grade:

The maximum size of the product aggregates is not critical, but rather is governed by what is practical in view of the packaging equipment, package size and ultimate use of the product. The product prepared in accordance with the preferred mode of carrying out the process of this invention usually consists of aggregates no larger than 20 US. mesh. However, coarser material can be prepared within the scope of the present invention.

EXAMPLE Essentially pure cyanuric acid powder is charged to a cyanuric acid compactor feed hopper by a feed screw :at ther ate of 375 lb./hr. This cyanuric acid powder has the following characteristics:

Characteristic: Value Cyanuric acid assay, percent weight 99.3 Ammelide-ammeline content, percent weight 0.1 Moisture, percent weight 0.05 Ammonium salts (as NH percent weight 0.02 Iron p.p.m 7 Screen analysis (cumulative) percent:

on 100 mesh (U.S) 1

on 200 mesh 9 on 300 mesh 70 Flow grade 5 Bulk density g./cc. 0.72

This fresh feed to the compactor feed hopper is fed along with 75 1b./hr. of coarse recycle and 350 lb./hr. of cyanuric acid fumes recycle. The resulting mixture of fresh feed and recycle is fed by screw feed from the cyanuric acid compactor feed hopper at a rate of 800 lb./ hi. to a Fitzpatrick Chilsonator compactor with 10-inch diameter grooved rolls 7 inches long operating with pressure at line of roller contact of 70,000 p.s.i. The compacted cyanuric acid issues from the bottom. of the compactor as corrugated flakes about 1 to 4 inch square and /4-lIlCl1 thick, directly into a cyanuric acid granulator. This granulator is a Fitzpatrick Fitz Mill operating with impact rotor turning 3600 r.p.m., so that production of coarse particles is relatively small. Granulator product falls directly into an air separator which is a 36-inch diameter Gayco Air Separator, operating on the principle of separation by air buoyancy acting against centrifugal force on individual particles. Coarse particles are withdrawn to a hopper and recycled back to the cyanuric acid compactor feed hopper. The air-lifted product is withdrawn and fed directly to a 2nd 36-inch diameter Gayco Air Separator from which dust is removed and recycled to the compactor feed hopper with the aid of a fan. The product is continuously withdrawn and used to fill packages or stirred in bulk.

The product is recovered in virtually quantitative yield and chemically unchanged. The physical characterstics are greatly improved and are listed below.

4 Characteristic: Value Screen analysis (cumulative),

percent:

on 20 mesh 5 on 40 mesh 19 on mesh 73 on mesh 90 on 200 mes-h 98 Bulk density g./cc. 0.95 Flow Grade 1 Flow grade (after 4 months drum storage) 1 Product is free-flowing, non-caking and suitable for automatic packaging operations in small containers.

TEST

The following demonstrates the improved flow properties when cyanuric acid is processed as in the above example. Mobility of cyanuric acid samples was evaluated by the test method previously mentioned. Cyanuric acid with flow times i.e. mobility, below 15 seconds, as determined by this test may be obtained by the subject process of compacting, and air classification. In the test, 250 grams cyanuric acid was introduced into a glass funnel with a 60 lip angle; 192 mm. internal funnel diameter; stem length, mm; and stem internal diameter, 15 mm. A finger was placed over the funnel outlet while the cyanuric acid was introduced. The test was started when the finger was removed, allowing flow to begin and a stop watch was started. The stop watch was stopped when the last cyanuric acid left the funnel stem outlet.

The odd numbered runs were made using typical crystal-powder purified cyanuric acid (CA) having a bulk density of about 0.7 g./cc. and similar to that used as the starting material in the above example. Each even numbered run was made using cyanuric acid from the same lot as that used in the preceding odd numbered run, but which had been subjected to the process of this invention.

CA Purity, Time to Pass Run No. CA Lot wt. percent Through Funnel,

Seconds 1 99. 7 Would not pass, 1 99. 7 5.5. 2 97. 1 Would not pass, 2 97.1 8.0. 3 98. 0 Would not pass, .3 98. 9 7.0. i 99. 8 Would not pass, 1 99. 8 7.5.

All samples that passed test had 90% or more of product particle larger than 200 mesh.

From the foregoing, it can be seen that a novel process has been devised whereby cyanuric acid can be obtained which is ideally suited for use in automatic packaging equipment. The example is intended as an illustration of the preferred mode of carrying out the invention, and is not to be construed as limiting the scope of the invention as claimed.

In the following claims, material described as finer than (designated) U.S. mesh is that which would pass through a screen of the designated mesh size, and material described as no finer than (designated) U.S. mesh is that which would be retained on a screen of the designated mesh size.

We claim:

1. The process for producing free flowing cyanuric acid which comprises feeding finely divided cyanuric acid between rollers exerting a pressure on the cyanuric acid of at least 25,000 psi, breaking the resulting compacted material into small pieces and air separating from fines a high flow granular product.

2. The process for producing free flowing cyanuric acid which comprises feeding cyanuric acid of which at least 70% is finer than 200 US. mesh between rollers exerting a pressure on the cyanuric acid of at least 25,000 p.s.i., breaking the resulting compacted material into small pieces and air separating from fines a high flow granular product of which less than 50% by Weight is finer than 200 U.S. mesh.

3. The process of claim 2 wherein the finely divided cyanuric acid feed contains less than 0.3% by weight moisture.

The process of claim 2 wherein at least 80% by weight of the cyanuric acid feed is finer than 200 U.S.

mesh.

5'. The process for producing free flowing cy-anuric acid which comprises feeding finely divided cyanuric acid, at least 80% of which is finer than 200 U.S. mesh, containing less than 0.2% by weight moisture, between rollers exerting a pressure on the cyanuric acid of at least 25,000 p.s.i., breaking the resulting compacted material into small pieces and air separating from fines a high flow granular product at least 90% of which is no finer than 200 U.S. mesh, and at least 98% of which is no finer than 300 U.S. mesh.

6. The process of claim 5 wherein at least by weight of the granular product is in the range of to U.S. mesh.

7. The process of claim 5 wherein the product is first air separated from particles larger than 20 U.S. mesh and then air separated from fines.

8. The process of claim 5 wherein the rollers exert a pressure of 60,000 to 80,000 p.s.i.

References Cited UNITED STATES PATENTS 3,070,318 12/1962 Blanchard 24l14 3,154,545 10/1964 Symes et al. 260-248 GERALD A. DOST, Primary Ex'aminer.

WALTER A. MODANCE, Examiner.

I. M. F. PAS], Assistant Examiner. 

1. THE PROCESS FOR PRODUCING FREE FLOWING CYANURIC ACID WHICH COMPRISES FEEDING FINELY DIVIDED CYANURIC ACID BETWEEN ROLLERS EXERTING A PRESSURE ON THE CYANURIC ACID OF AT LEAST 25,000 P.S.I., BREAKING THE RESULTING COMPACTED MATERIAL INTO SMALL PIECES AND SEPARATING FROM FINES A HIGH FLOW GRANULAR PRODUCT. 